A wide angle flat field microscopic objective of low power

ABSTRACT

Microscopic objective lens consisting of a first, a second and a third lens group arranged in that order from the object side and separated respectively by airgaps from each other. The first lens group is constructed by a cemented meniscus lens component with the air contacting surfaces thereof concave toward the object side and the second lens group is constructed by a meniscus lens element with the surfaces thereof concave toward the object side while the third lens group is constructed by a cemented lens component consisting of a lens element of negative refractive power arranged at the object side and a lens element of positive refractive power arranged at the image side. The absolute value of the focal length of the second lens group is selected to be greater than the focal length of the entire system and the absolute value of the radius of curvature of the surface of the second lens group at the object side is selected to be smaller than half the focal length of the entire system while the absolute value of the radius of curvature of the air contacting surface of the first lens group at the object side is selected to be greater than 0.15 times the focal length of the entire system and the Abbe&#39;&#39;s number of the lens element of the third lens group at the image side thereof is selected to be greater than that of the lens element at the object side by at least 25.

United States Taira [21] Appl. No.: 58,452

[30] Foreign Application Priority Data Aug. I4, 1969 Japan ..44/64374 [52] US. Cl. ..350/225, 350/175 ML, 350/177 [51] Int. Cl ..G02b 9/12, G02b 21/02 [58] FieldofSeareh ..350/175 ML, 176, 177, 225,

[56] References Cited UNITED STATES PATENTS 7/1966 Zeigler ..350/175 ML UX 2/1958 Bernhardt .....350/175 ML UX 8/1968 Judd ..350/177 X Primary Examiner-John K. Corbin '1 Mar. 7, 1972 Attorney-Kurt Kelman [5 7] ABSTRACT Microscopic objective lens consisting of a first, a second and a third lens group arranged in that order from the object side and separated respectively by airgaps from each other. The first lens group is constructed by a cemented meniscus lens component with the air contacting surfaces thereof concave toward the object side and the second lens group is constructed by a meniscus lens element with the surfaces thereof concave toward the object side while the third lens group is constructed by a cemented lens component consisting of a lens element of negative refractive power arranged at the object side and a lens element of positive refractive power ar ranged at the image side. The absolute value of the focal length of the second lens group is selected to be greater than the focal length of the entire system and the absolute value of the radius of curvature of the surface of the second lens group at the object side is selected to be smaller than half the focal length of the entire system while the absolute value of the radius of curvature of the air contacting surface of the first lens group at the object side is selected to be greater than 015 times the focal length of the entire system and the Abbes number of the lens element of the third lens group at the image side thereof is selected to be greater than that of the lens element at the object side by at least 25.

1 Claims, 2 Drawing Figures BACKGROUND OF THE INYENTION The present invention relates to a microscopic objective lens and more particularly to a microscopic objective lens having a magnification of about 4 and a wide field of view the image height of which can be greater than 0.6 times the focal length of the objective lens, wherein the image surface is flat while a high-resolving power is obtained.

Heretofore, it has been difficult to provide a microscopic objective lens of a magnification of about 4 which is simple in construction and produced at a low cost and has yet a flat and wide field of view and a high-resolving power.

The present invention aims at avoiding the disadvantages of the prior art microscopic objective lens described above.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel and useful microscopic objective lens of a magnification of about 4, which is simple in construction and produced at a low cost and yet has a high-resolving power as well as a wide, flat field of view.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, the objective lens consists of a first, a second and a third lens group arranged in the order from the object side and separated respectively by airgaps from each other.

In accordance with the characteristic feature of the present invention, the first lens group is constructed by a cemented meniscus lens component with the air-contacting surfaces thereof concave-toward the object side and the second lens group is constructed by a meniscus lens element with the surfaces thereof concave toward the object side while the third lens group is constructed by a cemented lens component consisting of a lens element of negative refractive power arranged at the object side and a lens element of positive refractive power arranged at the image side, and the focal length of the second lens group fll is selected to satisfy the following relationship:

where:

f focal length of the entire system of the objective lens If the absolute value If!!! is made smaller than the focal length f, curvature of field and coma are remarkably increased so that they can not be compensated for by means of other lens elements of the objective lens.

Further, radius of curvature r of the air-contacting surface of the second lens group at the object side thereof is selected to satisfy the following relationship:

If the absolute value [ml is made greater than the above value 172, the compensation for the curvature of field is made insutficient. To compensate for the above undercorrection of the curvature of field, the radius of curvature r, of the foremost surface of the first lens group must be made small. However, when radius of curvature r is made small, coma will be remarkably increased thereby deteriorating the quality of the objective lens.

Therefore, the absolute value of radius of curvature i li must be kept to satisfy the following relationship:

If the absolute value of lfli is made smaller than the above value of O. 1 5f, the coma resulting from the radius of curvature |r1| can not be compensated for by other lens elements of the objective lens.

Finally, the Abees numbers 1' 11 respectively of the front and the rear lens element of the third lens group must be selected to satisfy the following relationship:

If the difference I -v. is made smaller than the above limit 25, chromatic spherical aberration is remarkably increased so that it can not be compensated for by other lens elements of the objective lens.

An example of the microscopic objective lens is shown in the following table:

Focal length #28. Magnification Ab -4.0 Numerical aperture N.A.=0.l r. e.13 4. 1.2 1 r, 14.7 a, 2.5 n, L516 v. 64.0 r, 9.21 a, 4.1 1144 v, 44.7 r, -s.s1 a, 2 1 r, -10 a, 2.6 n,l.603 v, no I. 54.01 a. 1.3 1 0, 13.97 a, 2.1 11.1.699 v. 30.1 r. -13.s7 ".1487 v, 114.5

where:

r, radius of curvature of the respective surface each of the lens elements (i=1, 2, 8, arranged in the order beginning at the object side) d, thickness of lens element or airgap (i=l, 2 7, ar-

ranged in the order beginning at the object side) n, refractive index of lens element (i=l 2, 5, arranged in the order beginning at the object side) 1 refractive index of air v, Abbes number of lens element (i=1. 2, 5, arranged in the order beginning at the object side) As shown in FIG. 2 showing the aberrations of the above example, various aberrations are remarkably compensated for in the objective lens of the present invention.

I claim:

1. Microscopic objective lens consisting of a first, a second and a third lens group arranged in the order from the object side and separated respectively by airgaps from each other, wherein the improvement comprises said first lens group constructed by a cemented meniscus lens component with the aircontacting surfaces thereof being concave toward the object side, said second lens group constructed by a meniscus lens element with the surfaces thereof being concave toward the object side and said third lens group constructed by a cemented lens component consisting of a lens element of negative refractive power arranged at the object side and a lens element of positive refractive power arranged at the image side, said lens groups satisfying the following relationship:

where:

f focal length of the entire system fl! focal length of the second lens group r, radius of curvature of the respective surface each of the lens elements (i=l 2 8, arranged in the order beginning at the object side) :1, Abbe's number of the material each of the lens elements (Fl 2 5, arranged in the order beginning at the object side), and the lens satisfying the following table:

where:

Focal length Magnification Numerical apertur d, L2 d 2.5 d; 4.7 4 2 d, 2.6 d, 1.3 d, 2.1

r =radius of curvature of the respective surface each of the lens elements (i=1. 2. 8. arranged in the order beginning at the object side) 

1. Microscopic objective lens consisting of a first, a second and a third lens group arranged in the order from the object side and separated respectively by airgaps from each other, wherein the improvement comprises said first lens group constructed by a cemented meniscus lens component with the air-contacting surfaces thereof being concave toward the object side, said second lens group constructed by a meniscus lens element with the surfaces thereof being concave toward the object side and said third lens group constructed by a cemented lens component consisting of a lens element of negative refractive power arranged at the object side and a lens element of positive refractive power arranged at the image side, said lens groups satisfying the following relationship: -fII > f r4 < OR = f/2 r1 > OR = 0.15f Nu 5- Nu 4 > OR = 25 where: f focal length of the entire system fII focal length of the second lens group ri radius of curvature of the respective surface each of the lens elements (i 1, 2 --- 8, arranged in the order beginning at the object side) Nu i Abbe''s number of the material each of the lens elements (i 1, 2 --- 5, arranged in the order beginning at the object side), and the lens satisfying the following table: Focal length 28.4 Magnification -4.0 Numerical aperture 0.1 r1 -6.13 d1 1.2 1 r2 14.7 d2 2.5 n1 1.516 Nu 1 64.0 r3 -9.27 d3 4.7 n2 1.744 Nu 2 44.7 r4 -6.51 d4 2 1 r5 -10 d5 2.6 n3 1.603 Nu 3 38.0 r6 54.07 d6 1.3 1 r7 13.97 d7 2.1 n4 1.699 Nu 4 30.1 r8 -13.57 n5 1.487 Nu 5 84.5 1 where: di thickness of lens element or airgap (i-1, 2 --- 7, arranged in the order beginning at the object side) ni refractive index of lens element (i-1, 2 --- 5, arranged in the order beginning at the object side) 1 refractive index of air. 